1. Field of the Invention
The present invention relates to a leak tester that senses leakage from an airtight article, for example, an endoscope.
2. Description of the Related Art
For example, an endoscope is a reusable medical apparatus and must thus be washed and disinfected. In this case, if a pin hole or a connection in the endoscope is loose, a liquid such as water or a disinfectant may enter the endoscope during washing or disinfection to cause a failure in an electric element such as an optical fiber or a CCD. Thus, to prevent such a failure, a leak test must be carried out on the endoscope.
A common leak test method for an airtight article such as an endoscope comprises immersing the article into water, injecting pressurized air into the article, and checking for bubbles generated. However, this method requires a human operator to execute visual checks and thus fails to automate the leak test. As a result, a manual operation is constantly required.
Thus, it is common to use a method of pressurizing the interior of the endoscope to close up the endoscope and sensing a variation in the internal pressure to determine whether or not there is leakage, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-220110. However, this method requires a pressure sensor (gauge pressure plus absolute pressure) having a full scale for a pressure equal to or higher than that used for the pressurization. If the pressure varies insignificantly in response to leakage, time-consuming measurements are required in order to ensure accuracy.
Thus, Jpn. Pat. Appln. KOKAI Publication No. 4-221733 and Japanese Patent No. 3186438 disclose more accurate and prompt measuring methods based on a method using a differential pressure sensor are disclosed.
However, Jpn. Pat. Appln. KOKAI Publication No. 4-221733 discloses a measuring master (hereinafter referred to as a master) that measures a measured object retaining an initial pressure (the master has a volume almost comparable to that of the measured object). Accordingly, if the measured object is large or has a complicated shape, a considerably high cost is required to produce and maintain the master. Further, it is difficult to reduce the size of the apparatus.
In view of the above disadvantage of Jpn. Pat. Appln. KOKAI Publication No. 4-221733, Japanese Patent No. 3186438 discloses a differential pressure type leak tester that eliminates the need for a master by using a part of a pipe free from leakage, in place of a master.